Cyclist coasting down a hill cons. of energy

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Homework Help Overview

The problem involves a bicyclist coasting down a hill at a steady speed, with a focus on determining the power output required to climb the same hill at the same speed. The context includes concepts of energy, specifically kinetic and gravitational potential energy, as well as power calculations.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • Participants discuss the implications of coasting at a steady speed, questioning the presence of friction and its effects on the cyclist's motion. There is an exploration of the necessary forces acting on the cyclist while descending the hill.

Discussion Status

The discussion is active, with participants raising questions about the assumptions made regarding friction. Some guidance is offered regarding the necessity of accounting for friction when considering the cyclist's steady speed down the hill.

Contextual Notes

There is uncertainty regarding the presence of friction and how it affects the calculations. The original poster expresses doubt about the assumptions made in their calculations.

totallyclone
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Homework Statement


A bicyclist coasts down a 7.0° hill at a steady speed of 5.0m/s. Assuming a total mass of 75kg (bicycle plus rider), what must be the cyclist's power output to climb the same hill at the same speed?


Homework Equations


EK=1/2 mv2
EG=mgh
P=W/T


The Attempt at a Solution


I tried the question and this is what I got but I'm answer if this is right... not sure if there's a Force of friction though because I read the question and assumed there isn't any force of friction... but I'm unsure... :rolleyes:

P=W/T
P=-WGΔdcos180°/T
P=-WGvcos180°
P=-mgsin7.0°(5.0)cos180°
P=-(75)(9.8)sin7.0°(5.0)cos180°
P=448W
 
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Well if the cyclist goes down the hill with constant speed, then there must be some kind of force that's stopping him from accelerating, so you should account for it accordingly.
 
hi totallyclone! :smile:
totallyclone said:
A bicyclist coasts down a 7.0° hill at a steady speed of 5.0m/s. Assuming a total mass of 75kg (bicycle plus rider), what must be the cyclist's power output to climb the same hill at the same speed?
…
not sure if there's a Force of friction …

he couldn't coast (at a steady speed) if there wasn't friction, could he? :wink:
 
tiny-tim said:
hi totallyclone! :smile:


he couldn't coast (at a steady speed) if there wasn't friction, could he? :wink:

so...THERE'S FRICTION!?
 
yup! :smile:
 

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